1. Field of the Invention
The invention relates to a powertrain control system for controlling line pressure for an automatic transmission and for controlling the throttle position of a throttle-controlled engine using a feed-forward torque calculation.
2. Background Art
Contemporary vehicle powertrains include a throttle-controlled engine and multiple-ratio gearing in which the torque flow paths are controlled by fluid pressure-operated friction clutches and brakes. The management of the torque distribution through the gearing from the engine to a transmission-driven shaft is achieved by an electronic controller that responds to powertrain variables, including engine variables and driver commands.
The transmission typically includes a fluid pressure circuit with a solenoid valve for achieving a desired circuit pressure for fluid pressure-operated actuators for the clutches and brakes. In this way, ratio upshifts and downshifts are achieved in response to the powertrain variables.
The engine typically would include a driver-operated throttle valve connected mechanically to a driver-controlled accelerator pedal. Control systems of this kind may be seen by referring to U.S. Patent Nos. 6,171,211, 6,122,583 and 5,413,539. These patents, which illustrate the use of a controller having a throttle position sensor or a mass air flow sensor to quantify the engine torque demand, are assigned to the assignee of the present invention.
Vehicles that are equipped with an electronic throttle control system do not have a direct mechanical linkage between the accelerator pedal and the engine throttle. In such control systems, the driver demand for engine torque is generated by an electronic accelerator pedal assembly, which in turn generates a throttle angle command used by an electronic throttle actuator for the engine. A control system using an electronic throttle valve controller may be seen by referring to U.S. patent application Ser. No. 09/783,116, filed Feb. 14, 2001, entitled xe2x80x9cAutomatic Transmission Shift Controlxe2x80x9d, Attorney Docket No. FMC 1267 PUS. This application is assigned to the assignee of the present invention.
Engine torque is controlled by the system disclosed in the co-pending patent application to achieve a smooth torque transition during a ratio change and to reduce variations in shift quality from one shift to the next. The controller establishes a commanded ratio rate during a shift interval and compares it to the actual ratio rate to detect an error. The commanded engine torque is then established to reduce the error in a closed-loop fashion. The engine throttle position in the design of the co-pending application is achieved by an engine controller that responds to a commanded throttle position signal, in addition to spark control or fuel control, to achieve an output engine torque. The torque distributed to the transmission is managed by clutch and brake solenoids in a control circuit that is independent of the closed-loop control for achieving a commanded engine output torque.
Accurate control of the transmission control pressure for the pressure-operated clutches and brakes is necessary to avoid excess slippage at the clutches and brakes. Excess slippage would result in excessive clutch and brake wear. On the other hand, pressures that are too high create excessive parasitic pump losses in the transmission, which results in less than optimum fuel efficiency.
For optimal operation, the control pressure in the transmission should be scheduled as a function of engine torque. Since there are time lags associated with the pressure control, a leading indicator of engine torque is needed. This will make it possible for the transmission to respond very quickly to any changes in engine torque commanded by the operator before the change in engine torque actually happens.
In conventional transmissions, an instantaneous correlation between a command for engine torque and the actual development of the desired engine torque is difficult to accurately achieve using a mass air flow sensor as an indicator of torque demand. An air flow sensor detects changes in the amount of air induced into the engine only after the throttle has moved.
Since it is difficult with known control systems to anticipate engine torque changes adequately in advance, control pressure in the transmission is scheduled at an artificially high level in order to ensure that an adequate pressure margin is available for all operating conditions of the powertrain. This margin will prevent unwanted clutch and brake slippage if the torque requirements change more rapidly than the line pressure control can accommodate, but there is a resulting efficiency penalty. The more advanced an indicator of engine torque is, the less the margin must be.
It is an objective of the invention to provide a powertrain controller that uses a leading indicator of engine torque. This is obtained by a torque-based electronic throttle control system. The driver request for torque from an electronic accelerator pedal assembly is used to generate an engine torque request, which in turn is fed forward and used to generate a throttle angle for the engine. In the alternative, a driver request can be obtained using a vehicle speed control system if the powertrain uses a vehicle speed controller. The leading indicator of torque is used by a transmission control pressure controller for a multiple-ratio transmission to obtain the earliest possible indication of torque. The torque request is developed directly by the driver""s input at the accelerator pedal and not from the resulting movement of the engine throttle.
In an embodiment of the invention, the vehicle operator controls an electronic accelerator pedal to measure the operator""s request for engine torque, and an electronic throttle actuator controls engine throttle position. The controller includes a processor unit with stored algorithms for computing the leading indicator of torque as a function of pedal position.
The electronic throttle actuator communicates with the controller whereby the leading indicator of torque is distributed to the throttle actuator to effect a fast change of engine throttle position in response to a torque request.
The electronic powertrain controller includes a transmission control module for controlling fluid pressure in transmission clutches and brakes. The leading indicator of torque is distributed to the transmission control module whereby the pressure at the transmission clutches and brakes is maintained at an optimum level for smooth ratio change and improved transmission operating efficiency.